1. Field of the Invention
The present invention relates to a magneto-resistance effect element having a spin valve film and a magnetic head using thereof.
2. Description of the Related Art
Responding to a recent trend towards down-sizing and high capacity of a magnetic recording medium, an expectation for a magnetic head (MR head)taking advantage of magneto-resistance effect (MR) which enable to extract a large output is growing high. An MR head has a magneto-resistance effect element (MR element) taking advantage of a magneto-resistance effect film.
In a conventional magneto-resistance effect film, a ferromagnetic material such as a Ni-Fe alloy and the like which shows an anisotropic magneto-resistance effect (AMR) has been used. However, since a magneto-resistance change rate (MR change rate) of an AMR film is at most only about 3%, it is insufficient for a down-sized/high capacity magnetic recording medium. Therefore, a magneto-resistance effect film showing much high sensitivity in the magneto-resistance effect is demanded.
Responding to such a demand, a multi-layer film such as an Fe/Cr or a Co/Cu in which a ferromagnetic metal film and a non-magnetic metal film are alternately stacked under a certain condition and the neighboring ferromagnetic metal films are coupled anti-ferromagnetically, namely a so-called artificial lattice film, is ascertained to show a giant magneto-resistance effect. In an artificial lattice film, an MR change rate at most exceeding 100% is reported (refer to Phys. Rev. Lett., Vol. 61, 2474 (1988), Phys. Rev. Lett., Vol. 64, 2304 (1990)). However, since the artificial lattice film is high in its saturation magnetization, it is not suitable for an MR head.
On the contrary, in a magnetic multi-layer film of a sandwich structure of a ferromagnetic layer/a non-magnetic layer/a ferromagnetic layer, even when the ferromagnetic layers do not form anti-ferromagnetic coupling, there is reported an example that materialized a large magneto-resistance effect. That is, while, in one ferromagnetic layer among those which are interposed by the non-magnetic layer, an exchange bias is exerted to pin down magnetization, the other ferromagnetic layer is reversed in its magnetization through an external magnetic field. Thereby changing a relative angle between directions of the magnetization of two ferromagnetic layers disposed being interposed by the non-magnetic layer, a large magneto-resistance effect can be obtained.
Such a type of multi-layer film is called as a spin valve film (refer to Phys. Rev. B., Vol. 45, 806 (1992), J. Appl. Phys., Vol. 69, 4774 (1991) and the like). Although the change rate of the MR of a spin valve film is not so large as that of an artificial lattice film, but it reaches about 10% and is enough large when compared with a conventional AMR film. Further, a spin valve film can be saturated in its magnetization at a low magnetic field, therefore adequate for an MR head. In an MR head which uses such a spin valve film, a large expectation is mounted from a practical point of view.
Now, when an MR element is utilized, for example, in a magnetic head, it is known that magnetostriction constant of an MR film should be made as small as possible. That is, when the magnetostriction constant is large, due to stress during head processing or thermal distribution or temperature variation during operation, Barkhausen noise, popcorn noise, snapcrackle noise can occur. Therefore, magnetostriction constant of a spin valve film is preferred to be 1.times.10.sup.-6 or less.
A spin valve film is also being discussed to be applied in a magnetic recording device such as a magneto-resistance effect memory (MRAM). Even in an MRAM which uses a spin valve film, Barkhausen noise occurs when the magnetostriction constant is large. This causes an error during playback. Therefore, the magnetostriction constant of a spin valve film is preferable to be set at 1.times.10.sup.31 6 or less.
Besides, it is desirable to employ a material as large as possible in its MR change rate in a spin valve film. A spin valve film utilizing a ferromagnetic material containing Co is known to have a large MR change rate. However, the magnetostriction constant of a Co based magnetic alloy is almost without fail around 1.times.10.sup.-6 and it is said that the magnetostriction constant is difficult to be reduced below 1.times.10.sup.-6 with the Co based magnetic alloy only. Although, by adding a small quantity of element to a Co based magnetic alloy, the magnetostriction constant can be reduced, such addition of a small quantity of element induces a decrease of its MR change rate.
When an MR element is employed in a magnetic head, to improve sensitivity of a magnetic head, anisotropic magnetic field H.sub.K and coercive force H.sub.C of an MR film are preferable to be small. When H.sub.K and H.sub.C of an MR film are small, a larger output can be obtained at low magnetic field, and an MR head can be improved in its sensitivity. However, both of H.sub.K and H.sub.C of a Co based magnetic alloy are 10 Oe or more in almost case without fail. Therefore, in a spin valve film utilizing a Co based magnetic alloy, coexistence of a large MR change rate and an excellent soft magnetic property can be materialized only with difficulty.
Further, upon improving sensitivity of an MR head, a spin valve film is required to be increased in its MR change rate. However, only with control of constitutional material or its composition of a spin valve film, further increase of its MR change rate is considered to be very difficult.